The overall goal of this competitive renewal application continues to be to investigate the contribution of Insulin Receptor Substrate-1 (IRS-1) and IRS-2 to breast cancer progression. The IRS proteins are cytoplasmic docking proteins that function as essential signaling intermediates downstream of activated cell surface receptors, many of which have been implicated in breast cancer. As common intermediates of multiple receptors that can influence tumor progression, the IRS proteins are positioned to play a pivotal role in regulating the response of tumor cells to multiple microenvironmental stimuli. As a result, they are also prime candidates to be targets for interfering with the tumor-promoting signals that are initiated through these disparate receptors. For this reason, it is essential that we understand how these proteins function so that we can accurately predict the consequences of their expression for breast cancer patients and determine how they can be manipulated to interfere with breast cancer metastasis. Work performed in the applicant's lab during the current funding period revealed that metastasis is significantly impaired in the absence of IRS-2, but it is enhanced in the absence of IRS-1. Moreover, IRS-1 is inactivated in metastatic tumors. These findings, obtained using Irs-deficient mice and the PyV-MT mouse model of mammary tumor progression, are the first to establish unique roles for the IRS proteins in tumor progression. The hypothesis to be examined in this renewal proposal is that IRS-1 is a metastasis suppressor and its inactivation enhances tumor progression, whereas IRS-2 promotes metastasis by regulating signaling pathways that facilitate tumor progression. To examine this hypothesis, the applicant proposes to: 1) Investigate the requirement for IRS-1 inactivation in mammary tumor metastasis. The hypothesis that IRS-1 inactivation by serine phosphorylation facilitates metastasis will be examined;2) Determine the mechanism by which IRS-2 promotes mammary tumor metastasis. The hypothesis that IRS-2 regulates cap-dependent protein translation of metastasis-promoting genes, including VEGF, will be examined;and 3) Determine whether IRS-1 inactivation and IRS-2 activation are independent or cooperating events for breast cancer metastasis. The hypothesis that IRS-1 impedes metastasis by interfering with the pro-metastatic functions of IRS-2 will be examined. Metastasis is the leading cause of death for cancer patients and novel approaches to impede or treat metastatic disease are needed. In this proposal, one mechanism by which tumor cells promote metastasis will be examined with the long-term goal of developing better diagnostic methods or new therapies to prolong the lives of, or cure, cancer patients with metastatic tumors.